1. Field of the Invention
The present invention relates to a cathode-ray tube having a panel whose outside is flat and, more particularly, to a flat cathode-ray tube in which stress distribution at a fused portion of the panel and funnel is artificially changed to improve salvage rate of glass in a salvage process.
2. Description of the Related Art
As shown in FIG. 1, a cathode-ray tube generally includes a panel 1 set at the front thereof, a shadow mask 3 for selecting colors of electron beams emitted to the inside of the panel 1, a frame 4 for fixing and supporting the shadow mask 3, a stud pin 6 for fixing the frame 4 to the panel 1, a funnel 2 combined with the panel 1 with each other to maintain the inside of the cathode-ray tube in vacuum state, a spring 5 connecting the stud pin 6 and the frame, a tube-shaped neck 10 located at the back of the funnel 2, an electron gun 8 set inside the neck 10 to emit electron beams 11, an inner shield 7 combined with the frame 4 to shield external magnetic field such as terrestrial magnetic field acting on the emitted electron beams 11, a deflection yoke 9 fixing the exterior of the funnel 2 to defect electron beams 11, and an explosion-proof band 12 placed at the skirt of the panel 1.
As shown in FIG. 2A, both of the inside and outside of the general panel 1 have a specific curvature. Thus, images displayed are distorted because of the curvature of the outside so that people feel uncomfortable to watch them. Furthermore, severe reflection of external rays of light due to the curvature aggravates eyestrain. A cathode-ray tube proposed for solving this problem employs a panel structure whose outside is perfectly flat, as shown in FIG. 2B, to allow people to feel comfortable to see images display thereon. This structure (referred to as FCD hereinafter) is widely being used since it can realize flat images, being capable of removing distortion of images in an appropriate visual range and mitigating eyestrain in the consideration of the image floatation effects.
The cathode-ray tube is fabricated by passing through multiple processes including a process of forming a screen on the inside of the panel, a sealing process of fusing the panel 1 and the funnel 2 to each other using frit glass to seal them, and an exhaust process for making the inside of the cathode-ray tube with high vacuum. In addition, constituent elements such as the electron gun 8, shadow mask 3, frame 4 and inner shield 7 are set inside the cathode-ray tube. There may be generated a fail in a specific element during the fabrication process or after completion of the process or generated a fail in a specific process. In this case, it is required that a poor cathode-ray tube is salvaged.
FIG. 3 is a diagram for explaining a salvage mechanism of the cathode-ray tube. The neck of the cathode-ray tube is cut to cancel the vacuum state inside the cathode-ray tube, the band is removed, and to be mounted on a starting zone. Then, the frit is partially eliminated using nitric acid at an etching zone, and the nitric acid on the panel and funnel is removed by water at a cleaning zone. Here, lots of origins are generated in the frit. Furthermore, different stresses are created at the inside and outside of the panel, funnel and frit while passing through a first hot water zone and a cool water zone. Especially, the glass component is broken by tensile stress at the origins. The frit is detached up to a portion of the inside thereof where compressive stress exists because the tensile stress is applied to the outside thereof while passing through the first hot water zone and the cool water zone. Then, the tensile stress is applied to the inside of the frit and the compressive stress is applied to the outside thereof while passing through the cool water zone and a second hot water zone, thereby completely detaching the frit.
The conventional cathode-ray tube panel has the inner and outer surfaces having specific curvatures, as shown in FIG. 2A, to secure structural strength. Thus, its corner can have a thickness of less than 130% of that of its center. In this case, there is no problem in salvaging the cathode-ray tube. In case of the panel (FCD) whose outside is flat and whose inside has a specific curvature, as shown in FIG. 2B, however, its corner has a thickness of more than 170% of that of its center because its inner side has a curvature similar to that of the mask and its outside is flat in order to maximize the structural strength of the shadow mask. This increases the thickness of the panel to maintain the strength of the mask, but the panel structure is vulnerable to thermal stress. Especially, the distribution of the stress of the panel is not uniform. Moreover, the cathode-ray tube must go through furnaces to be fabricated when it passes through Stabi process for removing welding stress in combination of the shadow mask and the frame, the frit sealing process for fusing the panel and the funnel to each other, and the exhaust process for easily emitting electron beams. This makes stress structure of the frit glass more non-uniform. Plenty of breakage occurs in the salvage process for separating the panel and the funnel from each other due to the non-uniform stress structure. Furthermore, the non-uniform stress structure deteriorates the strength of the panel.
In case that the wedge rate of the panel is above 170%, tensile stress of the fused portion due to thermal shock in the furnaces becomes very large, to bring about xe2x80x9ccorner pullxe2x80x9d phenomenon that means breakage at the diagonal corners of the panel when the panel and funnel are detached from each other, as shown in FIG. 4. This decreases the salvage rate of the panel and funnel that conventionally accounts for 35-45% of the cost of the FCD-type tube. To minimize this breakage rate requires improvement in complicated furnace processes such as Stabi process, frit sealing process, exhaust process, etc. and, especially, management of the stress in the frit sealing process for fusing the panel and funnel to each other in fabrication of the cathode-ray tube. However, this needs exorbitant investment for improvement of temperature of the furnace and deteriorates productivity to increase the cost of products.
It is, therefore, an object of the present invention to provide a cathode-ray tube capable of being manufactured with high productivity without requiring an additional investment.
To accomplish the object of the present invention, there is provided a cathode-ray tube including an envelope having a neck, a funnel and a panel fused to the funnel by using frit glass, the outside of the panel being near flat, the inside of the panel having a predetermined curvature, in which 1.7xe2x89xa6T2/T1xe2x89xa62.3 when T1 is the thickness of the center of the panel and T2 is the thickness of the diagonal corner of the panel, and a panel inside tensile stress at the fused portion of the panel and funnel is less than xe2x88x921.3876x+128.24 (Kgf/cm2) when the size of the effective picture area of the cathode-ray tube is x(unit: cm).
When the size of the effective picture area of the cathode-ray tube is x (unit: cm), the panel inside tensile stress at the fused portion of the panel and funnel is preferably less than xe2x88x921.4625x+119.88 and more preferably less than xe2x88x921.487x+117.1.